1. Field of the Invention
The present invention relates to a method for manufacturing a photoelectric conversion device using a single crystal semiconductor or a polycrystalline semiconductor.
2. Description of the Related Art
Total production of solar cells in the world in 2005 was 1,759 MW, which is an increase of 147% as compared to that in the previous fiscal year. Single-crystal-silicon solar cells and polycrystalline silicon solar cells account for a large part of the production of solar cells.
Silicon semiconductors are resources that are widely used not only in the solar cell industry but also in the semiconductor industry for memories, microprocessors, and the like. Therefore, with the year-by-year increase of production of solar cells, the shortage of supply of polycrystalline silicon, which is the material of silicon, and the resulting rise in the price of a silicon wafer have become problems in the industry.
The thickness of a crystalline solar cell using silicon, which is needed to absorb sunlight, is only about 10 μm. Nevertheless, a silicon wafer actually manufactured as a product has a thickness of about 200 to 300 μm. That is, the crystalline solar cell has a thickness ten or more times as large as the thickness needed for photoelectric conversion, and thus the silicon wafer is far from being effectively utilized. Speaking of extremes, most part of the silicon wafer functions only as a structural body for keeping the shape of the solar cell.
While using such a silicon wafer which is thick enough, the crystalline solar cell is provided with a rough-surface structure for light trapping in order to effectively use incident light. Rough-surface structure is formed by using the characteristic of an alkaline solution of NaOH, KOH, or the like in which the etching rate is different depending on the crystal plane direction of silicon. However, it is difficult to form an ideal rough-surface structure by etching with alkaline solution, and thus a method in which a laser processing technology and chemical etching are combined has been disclosed (e.g., see Japanese Published Patent Application No. 2003-258285).